The SAVEPOINT statement sets a
named transaction savepoint with a name of
identifier. If the current transaction
has a savepoint with the same name, the old savepoint is deleted
and a new one is set.

The ROLLBACK TO
SAVEPOINT statement rolls back a transaction to the
named savepoint without terminating the transaction. Modifications
that the current transaction made to rows after the savepoint was
set are undone in the rollback, but InnoDB does
not release the row locks that were stored in
memory after the savepoint. (For a new inserted row, the lock
information is carried by the transaction ID stored in the row;
the lock is not separately stored in memory. In this case, the row
lock is released in the undo.) Savepoints that were set at a later
time than the named savepoint are deleted.

If the ROLLBACK TO
SAVEPOINT statement returns the following error, it
means that no savepoint with the specified name exists:

ERROR 1305 (42000): SAVEPOINT identifier does not exist

The RELEASE
SAVEPOINT statement removes the named savepoint from the
set of savepoints of the current transaction. No commit or
rollback occurs. It is an error if the savepoint does not exist.

All savepoints of the current transaction are deleted if you
execute a COMMIT, or a
ROLLBACK that
does not name a savepoint.

A new savepoint level is created when a stored function is invoked
or a trigger is activated. The savepoints on previous levels
become unavailable and thus do not conflict with savepoints on the
new level. When the function or trigger terminates, any savepoints
it created are released and the previous savepoint level is
restored.